1. Field of the Invention
The present invention relates to a method and an apparatus of evaluating the state of molecular orientation of a thin film having anisotropic molecular orientation such as a liquid crystal alignment film in which initial orientation is applied to liquid molecules, and for recording medium for such a method and an apparatus.
2. Description of the Related Art
To evaluate a thin film having anisotropic molecular orientation (anisotropic thin film), various types of methods have been proposed thus far. As for the method using visible light, there is proposed, for example, a method of measuring the incidence angle dependency of the intensity of reflection light generated when a plurality of wavelengths are incident (Japanese Patent Application Laid-Open No. Hei 5-5699 and No. Hei 4-329333). There are also proposed a method of measuring the dependency of the intensity of reflection light on incidence angle and on incidence orientation (Japanese Patent Application Laid-Open No. Hei 3-65637) and a method of efficiently measuring the dependency of the intensity of reflection light generated from incidence light having only S polarization component and that having only P polarization component, on incidence angle and incidence orientation (Japanese Patent Application Laid-Open No. Hei 8-152307). Further, there is proposed a method of determining a dielectric constant, a film thickness and a direction of a principal dielectric constant coordinate of an oriented part, and a dielectric constant and a film thickness of a non-oriented part while rotating a sample in a plane, from the incidence orientation dependency of the polarization state of reflection light (Japanese Patent Application Laid-Open No. Hei 9-218133).
According to the methods using visible light rays, it is possible to quantitatively evaluate crystal orientation equivalent to molecular orientation for an inorganic thin film having high crystallinity since the correlation between the crystal structure and optical anisotropy for most of thin films has already been known. According to the method disclosed by Japanese Patent Application Laid-Open No. Hei 08-218133, in particular, not only optical anisotropy but also the thickness of a sample can be determined.
An organic thin film, by contrast, has normally very low crystallinity and, therefore, it is difficult to determine molecular orientation from the optical anisotropy of the film. In case of a polymer thin film typically represented by a liquid crystal alignment film, in particular, it is considered that molecular chains are mutually twisted. Due to this, the optical characteristics of a basic unit forming a polymer chain does not necessarily accurately reflect those of a polymer chain. That is, the molecular orientation of a thin film having low crystallinity, i.e., a polymer organic thin film such as a liquid crystal alignment film cannot be determined by measuring the optical anisotropy using a visible light ray.
To evaluate the state of molecular orientation of an organic thin film, an infrared absorption spectrometry using a linearly polarized infrared ray is widely carried out. This method is disclosed by, for example, R. Arafune et al.: "Appl. Phys. Lett., 71, 2755(1997)". This method is intended to measure the variation of the intensity of the infrared ray with respect to the relative angle between the polarization orientation of an infrared ray which has passed through a sample and sample orientation. That is to say, this method is intended to evaluate orientation by detecting dichroism that infrared absorption amount varies with molecular orientation. However, the application of this method is limited to a film formed on a substrate, such as a silicon substrate and a calcium fluoride (fluorite: CaF.sub.2) substrate transmitting infrared rays. Since an infrared ray is not transmitted by a glass substrate, the molecular orientation state of a film, such as a liquid crystal alignment film, formed on a glass substrate cannot be measured by this method.
In recent years, infrared ellipsometry for evaluating wavelength dispersion of the polarization state of reflection light generated when an infrared ray is applied onto the surface of a thin film, has been developed. The evaluation of bonding state of a silicon substrate and a carbon film is disclosed (T. Heitz et al.,: "Appl. Phys. Lett., 72, 780 (1998)". In addition, a method of evaluating the film thickness and composition of a boronphosphosilicate glass (BPSG) on a silicon substrate is disclosed (R. Ossikovski et al.: "Appl. Phys. Lett., 65, 1236 (1994)). According to these methods, reflecting molecular orientation, a polarization state greatly changes at a specific infrared absorbing wavelength. Thus, information on chemical composition as in the same manner as infrared absorption spectrometry can be obtained. Besides, a sample on a glass substrate can be measured.
However, these methods are applicable only to an isotropic film.
As stated above, although the methods using visible light can be appropriately applied to an inorganic thin film having high crystallinity, they cannot be applied to the measurement of the molecular orientation state of an organic thin film. With the method using infrared absorption, the molecular orientation of a thin film formed on, for example, a glass substrate which does not transmit infrared cannot be measured. With the infrared spectroscopic ellipsometry, a sample on a glass substrate can be measured but a thin film having anisotropic molecular orientation cannot be evaluated.
Therefore, there exists no method of measuring the molecular orientation state of an organic thin film, such as a liquid crystal alignment film, having anisotropy and formed on a glass substrate under these circumstances.